John Calvin on Deuteronomy 30:8-10

8. And thou shalt return “Return thou therefore,” etc. — Lat. and obey the voice of the Lord. The copula which Moses here employs is equivalent to the illative particle; for he argues from their certainty of obtaining pardon, that they should not hesitate to return to God, nay, rather that they should set about it with a cheerful and ready mind; and then that they should constantly proceed in the course of obedience. But, when he now requires of the people the perseverance which he had just before declared to be given by God alone, we may at once infer that they deal foolishly who estimate the powers of man by the commands of God. Meanwhile, let us bear in mind this main point, that true conversion is proved by the constant tenor of the life; because we are redeemed, as Zecharias testifies, to this end that we should serve God, our Deliverer, “in holiness and righteousness all the days of our life.” (Luke 1:74, 75.)